What's That Bug? does not endorse extermination

Subject:  big silkmoth caterpillar
Geographic location of the bug:  Bangor, Maine
Date: 08/14/2019
Time: 03:47 PM EDT
Your letter to the bugman:  Hi! We rescued this caterpillar who was crossing the highway.  I’ve seen photos of it online with people saying it’s a Luna, but I’m thinking maybe Polyphemus?
How you want your letter signed:  Ryan and Emily

Pre-Pupal Luna Moth Caterpillar

Dear Ryan and Emily,
Distinguishing a Luna Caterpillar from a Polyphemus Caterpillar can be challenging, but we believe your caterpillar is a Luna Caterpillar.  The pink coloration is due to it being pre-pupal, and we have seen numerous images of pink pre-pupal Luna Caterpillars.  Luna Moth caterpillars, according to BugGuide, are:  “Larva lime-green with pink spots and weak subspiracular stripe on abdomen. Yellow lines cross the larva’s back near the back end of each segment (compare Polyphemus moth caterpillars, which have yellow lines crossing at spiracles). Anal proleg edged in yellow. Sparse hairs.”  Your individual is lacking the “yellow lines crossing at spiracles” that are present in Polyphemus Caterpillars.

Thank you so much Daniel.  What a tricky ID!  Much appreciated.
Update:  August 17, 2019
Bugman (Daniel)– our strangely-colored Luna caterpillar has made a cocoon by folding up some birch leaves in its fish tank terrarium.  I’m aware that it should be misted periodically so it doesn’t dry out…how often is that necessary?  How many days can you skip the misting, without it drying out to death?
Thank you again so much for the ID of this creature.  –Ryan
Hi again Ryan,
We do not raise caterpillars in captivity, but the problem with a terrarium is that it is cut off from external conditions.  Outdoors, the cocoon would be exposed to rain and other precipitation.  Another problem with raising caterpillars indoors is the stable temperature that occurs in modern homes, and this can effect emergence time which presents problems when adults emerge at a time of year that prevents release back into the wild (like an indoor emergence in the dead of winter).  The important consideration is not how often you mist, but when you mist.  If the captive conditions get too dry, the pupa might desiccate.  Trying to duplicate outdoor conditions in a protected environment is a goal.  Good luck.  
What's That Bug? does not endorse extermination
Location: Bangor, Maine

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